I overhauled the engine in my 05 3.7. ran fine before but lost a lifter, pushing 300,000 miles. runs fine when cold, but when it warms up it has what i would call a soft knock. doesn't miss but you can feel it and hear it, the engine sounds like it has an exhaust leak but it doesn't. this has got me baffled. I just retired form the automotive and semi trucks industries. any help would be appreciated, thanks